The parrot fish

A man went to a pet store to get a fish. He noticed a strange, colored fish and asked the owner what the fish was called.....
 “That’s a parrot fish,” said the owner. “It sings like a bird.” 
The man looked doubtful so the owner told him he could bring the fish back if he wasn’t satisfied. 

A week later the man returned to the store to return the fish saying...
 “You were right. The fish can sing. But, he’s horribly off key, and it is just too difficult to tuna fish.”